In　suspended　sludge　system,　efficient　enrichment　and　retention　of　anammox　bacteria　are　crucial　obstacles　in　mainstream　wastewater　treatment　by　anammox　process.　In　this　study,　anammox　bacteria　was　self-enriched　in　a　pilot-scale　suspended　sludge　system　of　two-stage　nitrification-denitrification　process　serving　municipal　wastewater　treatment.　With　the　low　ammonia　(NH4+-N)　of　9.3　mg/L,　nitrate　(NO3--N)　of　15.6　mg/L　and　COD/NO3--N　of　2.2　under　extremely　low　nitrogen　loading　rate　of　0.012　kg　N/m3/d,　anammox　activity　bloomed　after　its　abundance　increasing　from　5.9　x　107　to　4.6　x　109　copies/g　dry　sludge.　Significant　NH4+-N　removal　was　occurred　and　maintained　stably　in　the　denitrification　reactor　with　anammox　bacteria　accounting　for　1.13%,　even　under　temperature　decreasing　to　20.0celcius.　The　adequately　anoxic　environment,　efficient　retention　with　the　static　settlement,　and　NO2-　production　via　NO3-　reduction　provided　favorable　environment　for　anammox　bacteria.　This　study　demonstrated　the　feasibility　and　great　potential　in　mainstream　anammox　application　without　seeding　specific　sludge.